Fix string null in status_endpoint

roles/matrix-bridge-mautrix-whatsapp/templates/config.yaml.j2

@@ -10,7 +10,7 @@ homeserver:
     # The URL to push real-time bridge status to.
     # If set, the bridge will make POST requests to this URL whenever a user's whatsapp connection state changes.
     # The bridge will use the appservice as_token to authorize requests.
-    status_endpoint: "null"
+    status_endpoint: null
 
 appservice:
     # The address that the homeserver can use to connect to this appservice.